net: dsa: do not skip -EOPNOTSUPP in dsa_port_vid_add

Currently dsa_port_vid_add returns 0 if the switch returns -EOPNOTSUPP.

This function is used in the tag_8021q.c code to offload the PVID of
ports, which would simply not work if .port_vlan_add is not supported
by the underlying switch.

Do not skip -EOPNOTSUPP in dsa_port_vid_add but only when necessary,
that is to say in dsa_slave_vlan_rx_add_vid.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/port.c

@@ -382,8 +382,8 @@ int dsa_port_vid_add(struct dsa_port *dp, u16 vid, u16 flags)
 
 	trans.ph_prepare = true;
 	err = dsa_port_vlan_add(dp, &vlan, &trans);
-	if (err == -EOPNOTSUPP)
-		return 0;
+	if (err)
+		return err;
 
 	trans.ph_prepare = false;
 	return dsa_port_vlan_add(dp, &vlan, &trans);

net/dsa/slave.c

@@ -1082,8 +1082,11 @@ static int dsa_slave_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
 			return -EBUSY;
 	}
 
-	/* This API only allows programming tagged, non-PVID VIDs */
-	return dsa_port_vid_add(dp, vid, 0);
+	ret = dsa_port_vid_add(dp, vid, 0);
+	if (ret && ret != -EOPNOTSUPP)
+		return ret;
+
+	return 0;
 }
 
 static int dsa_slave_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,